Method and apparatus for preloading helicopter rotor shaft bearings



Aug. 12, 1952 KELLER 2,606,361

J. R. METHOD AND APPARATUS FOR PRELOADING HELICOPTER ROTOR SHAFT BEARINGS Flled June 21, 1949 2 SPEETS-SHEET l INVENTOR. JOfl/V E. 16 4156 Aug. 12, 1952 Filed June 21, 1949 J. R. KELLER METHOD AND APPARATUS FOR PRELOADING HELICOPTER ROTOR SHAFT BEARINGS 2 SHEETS-SHEET 2 INVENTOR. J0/-//V P. K5445? iazrf Patented Aug. 12, 1952 METHOD'AND APPARATUS-FOR PRELOAD- ING. HELICOPTER Boron SHAFT. BEAR.-

u INGS.

. John a. Keller, NewCar'lisle, Ohio Application June 21, 1949 Serial No. 100,520

.2 Claims. (Cl.'29 148.4)

(Granted "under the act of March 3 .-'188,3, ,-"as; I

amended 'April v30, 1928; 370 0.. G. -75?) .The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of any royalty thereon.

This invention relates to a method and apparatus for pre-loading the ball bearings which carry the thrust load of a helicopter rotor shaft, particularly in the. Sikorsky R- (Commercial 3-51) series of helicopters.

One object of the invention is to provide a method and apparatus whichsimplifies the task, saves time and simulates the pre-load under actual operating conditions. A pre-load is necessary to reduce sudden compressive stresses upon the steel balls of the ball bearings, from which the balls might crack. Such failure would be very dangerous to the aircraft. p

Another object is to provide a method and apparatus through which the degree of pre-load is always accurately measurableand under the control of the operator.

In the drawings:

Fig. l is an isometric view of thefazimuth or .stationary star which contains the'bearings to be adjusted. Shown in operating positionthereon are my jig, a torque wrench (in dashed lines) attached thereto, and a micrometer caliper in the position to obtain one of the necessary dimensions.

Fig. 2 is a side elevation of the stationary star shown in Fig. 1, showing my jig in place in the hub. The details of the star are shown'in dashed lines. 6

Fig. 3 is a plan view of my jig or fixture.

Fig. 4 is a fragmentary sectional view of the entire rotating star assembly as itis ready to operate on a'helicopter. The bearings which are to be adjusted are shown in vertical section.

The bearings to be pre-loaded are shown in Figs. 2 and 4 in which 5 is the upper bearing in use and l is the lower. These are reversed in Fig. 2 because this figure shows the stationary star l 2 inverted from the position occupied in Fig. 4.

Fig. 1 shows the azimuth star I2, the center of which is occupied by the upper plate I 3 of my fixture M. The plate 13' is shown in plan view in Fig. 3, the jig l4 itself appearing in side eleva- Y tion in Fig. 2. The fixture includes a bottom plate I5 identical with the plate [3 except that the latter bears a nut is which is welded to a boss I"! centrally located on the plate I3. Four or more bolts l8 join the top plate l3 and bottom plate I 5. Each plate has a U-shaped cut-out portion I!) which is intended for the accommodation of a micrometer caliper 8. A torque wrench 9 fitting the nut I6, is also necessary to rotate the fixture l4 so that preload can be measured.

In .order'to understand the method primarily assembling or of repairing a helicopter-rotor such as is partially illustrated in Fig. 4, the structure of such a rotor will now be described.

At the base of Fig. 4, I2 is the stationary star and above it a rotating star 22. The two stars are held in contact by a retainer ring 23. through which cap screws 24' extend. The drive shaft (not shown) which drives the rotating star 22;, would extend upward through a ball socket 25 which is mounted in races 26 and 27. The races are held down by a thrust. ring .28 through which eittend cap screws 29.v An oilwick :30. and oilhole 3001. are provided to. lubricate the foregoing parts.

The ball bearings 6. and: lwhich. are tobe ad.- J'usted are separated by an inner race. spacer 2| and an outer race spacer 20. The outer race spacer 20 is clamped stationary within the .stationary star I2 while the. inner" race spacer- 2| rotates with the rotating star22.

Stresses on the upper bearing races 39 and 40, inner and outerrespectiVely and the lower bearing races 4| and 42, inner and outer, respectively are mostly vertical and may be-eXerted either downward or upward. There is very littleradial stress originating as such; howeverwhen there; is

a down-pressing movement on the'rotating star 2 2. it-is ,ransferredto tliestationary star I Zby crossing overfrom one race to the other; horizontally through the balls. The pre-load should therefore be applied vertically rather than radially..v .The pre-lcad is maintained on the races 39, 40, 4| and 42 and balls I 0 and H by the cap-screws 24 exerting force through the retaining ring 23- ,against. a shoulder or boss 3| on the underside of the rotating star 22., The mount of pre-loading is; regulated by the thickness of shims 5| and 5 I aibetween the races 40 and 42 at one side thereof inserted in the horizontal position. The pre-load soselected is maintained by the presence of a cylindrical shim 34, the proper thicknessof-wh-ich is. deterrmined by micrometer readings to be obta-ined as later described. Theprinciple of pre-loa'ding. rests upon the difierence inthickness ofthe shiimning of the inner and outer races. When the amount of shimming between the outer races is:increased, the pre-load is increased; When theamount of shimming between imierraces isincreased, the amount of pre-load is decreased.- "The shimsfil and 51a when in the'positionshown' in FigL 4 ai'e shown in pre-load increasing position. If they were placed on the inner spacer 2|, they would decrease the l re-load. This action is due to the construction of the ball races and is shown in Fig. 4. There is an absence of shoulder at points 35 and 36 of the lower and upper races respec- .020" from both the top and bottom. The faces should be held parallel.

3. Measure the liner 3! for depth with a micrometer depth gage.

4. Measure the stack of bearings 6-1-20 with a micrometer caliper 8 with the outer spacer 20 in place. The liner 3'! should measure .003 to .005 of an inch less than the stack reading. If it does not, add the required amount of shim 33 at the top.

5. Install the stack of bearings 6 -1-40 in the stationary star, put the retainer ring 32 and bolts 50 into place.

6. Ascertain the pre-load of the bearings, using the fixture l4.

7. Install and center the pre-load fixture l4 on the inner races 39-4! of the bearings 6--'l with thenuts on the bolts l8, facing up. To insure even tightening, torque the four bolts l8 holding the fixture together to 20 pounds.

8. Measure the existing pre-load. Where available, use a sensitive torque wrench 9 (-150" pound range). The pre-load should be to pounds. If the pre-load is over 25" pounds, shim between the inner races 39-4I; if the preload is under 15' pounds, shim the outer races I shoulder or boss 3| on the base of rotating star.

11. The depth on the shoulder 3| on the rotating star should be .003" to .005 less than the height of the bearing stack 6-12l to insure proper pinch on the inner races 394l of the bearings to maintain their required pre-load.

Add shim 34 on top or bottom of bearing stack on'inner races 39- to obtain these measurements;

121 Support the stationary star properly. Place oil retainer rings 5252a in position and press rotating star assembly through until the inner races 39- of the bearings seat in the cylindrical liner53 of the rotating star as shown in Fig. 4.

13. Install retainer ring 23 with bolts 24. Tighten and resafety the nuts with safety wire.

14. Check pre-load after assembly. The preload will generally be from 0" to 5" pounds less after assembly than the pre-load previously measured, since the fixture has a more direct clamping action than the retainer ring on the rotating star.

1 I claim:

1'. The method of applying a proper pre-load to 'alstaok of ball bearings having inner and outer racesand spacers and liners in the stationary starof a helicopter rotor which star has a housing, said method consisting substantially of removing stock from the bottom edge of the liners so that they do not protrude beyond the housing portion of the star, measuring the outer liner micrometrically for depth, measuring the stack of bearings micrometrically, the outer spacer being in place, adding an amount of shim, if required, at the top to make the liner measure a few thousandthsof an inch less than the stack reading, installing the stack of bearings in the stationary star, putting a retainer ring and bolts into place to retain the stack therein, ascertaining the preload of the bearings, installing and centering a preload fixture on the inner races of the bearings, the nuts of the bolts of said fixture facing up, torqueing the bolts together to identical pressure, measuring the existing preload by rotating the fixture while observing the torque required to do so, shimming between the inner races if the preload is too small, shimming between the outer races if the preload is too great, measuring the height of the bearing stack while under preload, measuring the depth of shoulder on the base of the rotating star, shimming the bearing stack on the inner races to make the depth of shoulder a few thousandths of an inch less than the height of the bearing stack, pressing the rotating star through the stationary star until the inner bearing races seat within the rotating star, and then installing a retainer ring to hold the stationary star assembly withinthe rotating star and clamping said ring into position.

2. A device for pre-loading ball bearings having vertical inner and outer races to a controllable degree of pre-load comprising an upper stiff circular plate of a diameter substantially that of the inner races, said plate being indented at one area of its circumference by a deeply cutout portion through which a micrometer caliper can be extended, a substantially identical lower plate also having a similar cutout portion in registry with the upper plate as regards position of the cutout portions, more than two bolts, each one of which extends through both the upper and lower plates at equispaced radially intermediate locations, and means for engaging a torque wrench, said means being located at the center of the top surface of the upper plate whereby the entire device and the inner ball bearings braces may be rotated to measure a preload by the torque necessary to rotate the assembly when said torque is applied to the torque wrench.

JOHN R. KELLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,310,372 Oserowsky Feb. 9, 1943 2,446,621 Thiry Aug. 10, 1948 OTHER REFERENCES Pp. 33, 40, 45, 94 and 95 New Departure Hand Book, 15th edit., June 1941. Pub. by New Departure Div. Gen. Motors Corp., Bristol, Conn. 

